The present invention relates to an electronic switch used in a low noise block down converter for selecting satellite vertical or horizontal polarization signals. The electronic switch utilizes an electronic pulse technique to obtain advantages of high reliability and optimal effects.
The present satellite television receiving system commonly uses a mechanical switch to select the horizontal and vertical polarization signals. In the example of the North-American satellite television system (as shown in FIG. 5), the feed horn 41 of the low noise down converter (LNB) comprises a servo motor 42 which is activated by signals of ground, +5 V and a pulse Width supplied by a TV receiver 43. One end of the servo motor 42 is connected to a probe 44 so that when the servo motor 42 is rotating, the probe 44 can be forced to rotate to receive the vertical or horizontal polarization signal. However, such a mechanical switch has disadvantages as follows: (1) the reliability of the servo motor is low, particularly in winter, the water flowing into the motor (if any) will be condensed such that the motor is possibly hard to be rotated; and (2) the servo motor is a separately located means, therefore, there are needed three cables to receive the ground, 5 V and pulse width signals from the receiver 43, so that the cost of the system will be higher and the construction thereof will be more complicated.